Fiber optics are commonly used in magnetic field reservoir monitoring systems to detect and determine properties of inhomogeneities in a target reservoir. The optical signal passing through a fiber optic receiver in the absence of any monitored inhomogeneity in the reservoir—such as water flood, steam, gas, and carbon dioxide—is altered in the presence of any such inhomogeneity. The change in the optical signal produced by the presence of the inhomogeneity is then used to infer the properties of the monitored inhomogeneity.
In the absence of any inhomogeneity, fiber optic receivers receive signals directly from a signal source, such as a transmitter. These direct signals are typically strong because they have experienced minimal formation penetration. Once an inhomogeneity—such as a water flood—is introduced to the environment, at least some of the signals received by the fiber optic receivers have reflected off of the inhomogeneity. These signals, called scattered signals, may be significantly weaker than the direct signals. As a result, they can be difficult to distinguish from the direct signals and other noise. This disparity in signal strengths necessitates a large dynamic range in the electronics associated with the fiber optic system, which is often not practical in downhole environments.
It should be understood, however, that the specific embodiments given in the drawings and detailed description thereto do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed together with one or more of the given embodiments in the scope of the appended claims.